The N.S.A. is not just intercepting the communications of Americans who are in direct contact with foreigners targeted overseas, a practice that government officials have openly acknowledged. It is also casting a far wider net for people who cite information linked to those foreigners, like a little used e-mail address, according to a senior intelligence official.

….To conduct the surveillance, the N.S.A. is temporarily copying and then sifting through the contents of what is apparently most e-mails and other text-based communications that cross the border. The senior intelligence official, who, like other former and current government officials, spoke on condition of anonymity because of the sensitivity of the topic, said the N.S.A. makes a “clone of selected communication links” to gather the communications, but declined to specify details, like the volume of the data that passes through them.

….The official said that a computer searches the data for the identifying keywords or other “selectors” and stores those that match so that human analysts could later examine them. The remaining communications, the official said, are deleted; the entire process takes “a small number of seconds,” and the system has no ability to perform “retrospective searching.”

The official said the keyword and other terms were “very precise” to minimize the number of innocent American communications that were flagged by the program.

The justification for this revolves around a close parsing of the word “target”: As long as no Americans are specifically targeted, NSA can trawl through our email as much as it wants. After all, the keywords it’s looking for may come from emails we send, but they’re targeted at foreigners:

The rule they ended up writing, which was secretly approved by the Foreign Intelligence Surveillance Court, says that the N.S.A. must ensure that one of the participants in any conversation that is acquired when it is searching for conversations about a targeted foreigner must be outside the United States, so that the surveillance is technically directed at the foreign end.

Maybe so. But if you send an email to a pal in Berlin, be careful. Mention the wrong name or talk about the wrong subject, and you could end up in the NSA’s dragnet.